The present invention relates to a method and apparatus for controlling a light emitting element. The invention can be used in light emitting diode (LED) arrays and liquid crystal over silicon pixel arrays.
Conventionally, LEDs have been driven using analog drive apparatus. Such apparatus suffers from a number of disadvantages. Distribution of analog current or voltage to a plurality of pixels is prone to noise induced by any digital switching of nearby control signals. Multiple analogue distribution circuits can be used to reduce bandwidth requirements, but these have inherent mismatching due to the variability in transistor characteristics on standard semiconductor manufacturing processes. When an analogue value is stored at a pixel, no more than a few percent of the original value should be lost in a typical (60 Hz) frame refresh time of 16.666 ms. This is difficult to achieve because of inherent temperature and light-induced charge leakage of capacitive storage nodes. The transfer of analogue voltage or current to an LED may be affected by threshold voltage variability across a plurality of pixels. Finally, LED devices do not have linear voltage-to-light or current-to-light transfer characteristics.